biscuit joining and clamping question

[promhandicam]

I am starting to attack the pile of boards that I recently took delivery of to make firstly a cabinet to for the TV and HiFi. I need to join three boards 20 mm thick to get the width I need +/- 50 cm. I intend using #20 biscuits and cutting the slots with the a biscuit cutter on the router (don't have a dedicated biscuit jointer - yet :wink. My question is - how close together should the biscuits ideally be? The boards are about 2m long. I've had a look through previous posts but still can't find an answer to this.

Thanks,

Steve

 

[Philly]

Steve
If you are edge jointing the boards you really only need biscuits to provide positive location when gluing up-the wood-to-wood joint will be plenty strong. So every 300/400mm should be plenty.
Hope this helps
Philly

 

[Johnboy]

Norm always spaces them 8-9 inches apart. I always put them nearer the underside face of the joint. In a 20mm thick board I would cut the centre of the slot about 12mm from the top. Less chance of the biscuits showing on the top of the board after a while. They are not really needed at all if the joints are good, the glue is plenty strong enough but they do help alignment.

John

Edit. Philly types faster than me!!

 

[superunknown]

As said by Philly

I have jointed tons of tops/panels without them, but putting them in makes life a ton easier.

 

[Scrit]

I'll play the devil's advocate if I may. Why do you need to biscuit at all? If you're joints are straight then the glue will actually have more strength than the timber, so I don't see the need.....

Scrit

 

[engineer one]

maybe the question from scrit should be what kind of clamps do you have, and how many???

in principal he is right and he should know. :roll:

however i guess a lot depends upon what glue you are using, in your local temperatues, as to what the open time is.

remember that if you are actually not going to use biscuits, then you will need to make "cauls" to hold the wood flat. these are curved boards that you clamp from each side (top and bottom).

however working alone, and with a short glue open time, then biscuits do have some advantages but a number of people have mentioned recently that too close to the top, the biscuits "show" or can do so i agree below halfway to the bottom.

i would suggest that 250 centres would be ideal, and maybe helpful.

paul :wink:

 

[Anonymous]

I would agree that biscuits are not actually necessery for strength but do aid alignment.

Having spent more time than I care to remember fighting to get panels aligned in sash cramps (before I got a Plano system) I think I would go with the biscuits!

Oh, and about 200mm apart

Brad

 

[promhandicam]

Thanks all for your thoughts.

. . . what kind of clamps do you have, and how many?

Perhaps this is more of the issue. I don't actually have any sash cramps at the moment - I only have short F and G clamps. I've been out this morning to see what I could find on the second hand market - without success. I will now have to go and pay top whack in one of the european shops in town to get some reasonable clamps. This is going to be an expensive business

I'll play the devil's advocate if I may. Why do you need to biscuit at all?

My thoughts for using biscuits were to help primarily with alignment during assembly rather than for strength. For gluing up I will be using the last of my Gripfill Wood Adhesive which I brought with me from the UK. I'm not sure what is available locally but will doubtless soon find out.

Thanks again - I'll let you know how things progress with some WIP pics.[/quote]

 

[engineer one]

ok mate so don't spend the money on too many "european clamps."

go for proper old fashioned work.

build a locator box. one straight edge the length of the finished boards, on either side.
make some curved cauls, and use your f and g clamps. wedge the boards in the locator box, and then clamp with the cauls and clamps.

just put some paper preferably waxed under each joint to catch the glue squeeze out.

 

[engineer one]

so to add, cut a baseboard which is about 60cm wide.
put two straight lengths on either side, screw down, and make sure they are equally straight all along.

next cut about 12 wedges (double wedges) for each side, being 2metres long.

then cut some bits of 50mm x with a slight hump in the middle.

place along the 2metre length at about 300 distance if you can. with one at each end. clamp using f and g clamps. start in the middle and work out. but do not tighten fully.

then wedge the sides, finally tighten f and g clamps.

hope this saves you money :lol: :twisted:

paul :wink:

 

[Scrit]

Remember that if you are actually not going to use biscuits, then you will need to make "cauls" to hold the wood flat.

Really? Cauls are used for veneering, I'd say. If your jointed edges are square why would you need cauls? OK, then what about using a rubbed joint - something which can be achieved with hide and PVA alike - all that needs is a few laths to lay up against the wall:

All these are from a book published in the 1920s

or if you don't have cramps and need to make your own (see Fig. 21):

The wedge board works pretty well - or it did when I started out and couldn't afford any sash cramps - just a bit slower and more fiddly to use. There's also the method of using pinch dogs at the end of your boards and a single sash cramp in the middle:

although this does work better if you can shoot the joints slightly hollow on one side

a number of people have mentioned recently that too close to the top, the biscuits "show" or can do so I agree below halfway to the bottom.

I'd say that problem is possibly also related to sanding. Take a compressed and very dry biscuit, stuff it into a tight-fitting slot then squirt in some wet glue and the fibres of both the biscuit and the timber around it will swell. whilst it will take 24 hours or less for the glue to set fully, it will probably take a few days for the timber to reach equilibrium, so if you sand it too soon the timber between the biscuit and the surface will continue to shrink and leave you with a nice little biscuit-shaped shadow..... This matter has been discussed on FWW Knots many many times and that's not just my conclusion, but the general concensus over there, too.

To the OP, don't take my comments too much to heart. Biscuits are as valid a method of keeping a long, narrow joint in alignment as the more traditional loose spline or tongue and groove.

Scrit

 

[woodbloke]

Agree with Phill and others - about 200-250mm spacing is about right though its not critical. Provided boards are shot fractionally hollow biscuits are not really needed either...I 'spose its just belt and braced really - Rob

 

[Sgian Dubh]

This matter has been discussed on FWW Knots many many times and that's not just my conclusion, but the general concensus over there, too. Scrit

I suspect you may in part be referring to me, Scrit, as I've been involved in some of those debates. I might, in fact, have been one of the first on that forum to alert other forum users to the rugby ball shaped depressions that can show when biscuits are used in edge joints. I'm guessing now, but I think I may have first mentioned this phenomenom on that forum back in about 1999. I think I first noticed the depression forming tendencies of biscuits in the mid or late '80's.

All that you say is true. The wood is pooched up if water based glue is introduced to both the edge faces of the joint and the groove part of the biscuit joint. The biscuits at some point during their manufacture I understand are steamed and hydraulically compressed. It's one way of ensuring they swell sufficiently to make a tight joint with their wee groove when moisture is added to the mix. In other words they're not designed for use with epoxy resins and polyurethane glues (for example) because they don't have water in them to swell the biscuits.

In any event, I always recommend to those that are inexperienced with slab glue ups done with water based glues, whether using biscuits or not, to wait for about a week after removing the clamps so that all the moisture introduced into the area can leave it. This allows the swollen timber to shrink properly again to match the rest of the panel glue up's moisture content.

Doing this means that the oval depressions are unlikely to appear later, and nor do the characteristic glue line furrows that can also show up. Allowing sufficient time between glue up and polish prepping I find means that the biscuits can be placed centrally in the thickness. My experience that the sometimes suggested advice to put the biscuits towards the bottom face of the joint is a bit of a canard. The wood still swells when moisture is added. Planning the job allowing sufficient time for the moisture to leave the wood seems to work best.

I see nothing fundamentally wrong with using biscuits in edge joinery. They're like splines, tongues and grooves, dowels, etc., that have been around and used for centuries with success. Where I do find them a bit of an irritant is during the actual glue-up. They're fiddly and slow down the process meaning it takes longer to get the clamps on, which can be bad news if the glue has skinned off before you can get pressure on.

Regarding the original question about spacing-- about 250 mm to 370 mm usually works pretty well. Just make sure you don't cut through one when you trim the top to length, ha, ha. Slainte.

 

[Paul Chapman]

In any event, I always recommend to those that are inexperienced with slab glue ups done with water based glues, whether using biscuits or not, to wait for about a week after removing the clamps so that all the moisture introduced into the area can leave it. This allows the swollen timber to shrink properly again to match the rest of the panel glue up's moisture content.

Doing this means that the oval depressions are unlikely to appear later

They did a very good demonstration of this on The Woodworking Channel http://www.thewoodworkingchannel.com/ using moisture meters to show how the panels had swelled in the areas of the biscuits and how the swelling reduced over a few days if left to dry out properly. Well worth watching if they repeat it.

As has been said, simply leave the panels for a few days for the moisture to dry out and there won't be a problem.

Cheers :ho2

Paul

 

[seaco]

8 to 9 inches works fine for me... Oh! Matron....

 

[Inspector]

I don't use biscuits to align wood for panels, but I don't do wide panel glue-ups in one step. I joint and thickness my boards thick, and then glue only 2 or 3 together keeping them under 12" / 300mm (the width of my thicknesser). Once the glue is cured I run them through the thicknesser to final size and touch up the edges if needed then glue those panels to make the final widths after trimming. It gives me fewer joints to keep aligned at any one time resulting in a panel that requires less to smooth and finish.

It isn't a method for volume production but for the amateur it's a good option.

 

[engineer one]

sorry scrit i now know it was the wrong word "caul" but it did bring out the info for which i too thank you.

your pictures were worth a thousand of my words.

paul :wink:

 

[promhandicam]

Thank you everyone for your contributions. To Scrit and Engineer One - I liked the idea of using wedges to hold things in place but as I have a number of different projects coming up, decided that the versatility of clamps would be better. I'd actually thought of using ratchet straps which I've done in the past for bigger assembly jobs but they are a bit fiddly - especially if trying to keep multiple pieces flat.

So I went off and had what I thought was a right result - 6 of these for the equivalent of £4.50 each:

They are made, inevitably, in china but have a max opening of 50cm which is what I was looking for and seem to be fairly solid with no slipping of the movable jaw.

I also managed to get a bottle of Bostik (sorry ColinC) Agobois Normal - Colle Vinylique which is a French import rather than the locally produced glue which is of decidedly dubious quality. According to the label, the Bostik has a long open time - 30 min at 20C.

So the plan for today is to glue up the boards, using biscuits at approx 250mm centres for ease of alignment. I will then leave the boards at least a week before sanding. Will post some WIP as promised in the projects forum when there is a bit of progress.

Salutations !

Steve

 

[Colin C]

HI Steve

PVA type Bostik is ok but I was talking about the type that is like contact glue :wink: .

You should be ok with what you have got

 

[promhandicam]

Oh dear. My maths failed me I somehow got it into my head that my 3 boards together came to about 49cm but they don't - more like 59cm

So I have six shiny new 50 cm claps - which will still be useful just not for the job they were bought for. So time for Plan 'b' - and a big thanks to Scrit and Engineer One for saving the day :lol:

I take it you had in mind something like this:

All the best,

Steve

(I've modified the original subject, to better reflect the thread)